US10101279B2 - Method of diamond color grading - Google Patents

Method of diamond color grading Download PDF

Info

Publication number
US10101279B2
US10101279B2 US15/083,308 US201615083308A US10101279B2 US 10101279 B2 US10101279 B2 US 10101279B2 US 201615083308 A US201615083308 A US 201615083308A US 10101279 B2 US10101279 B2 US 10101279B2
Authority
US
United States
Prior art keywords
diamond
color
raman
diamonds
peak
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related, expires
Application number
US15/083,308
Other versions
US20180031487A1 (en
Inventor
Dong-Shyogn Pan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to US15/083,308 priority Critical patent/US10101279B2/en
Publication of US20180031487A1 publication Critical patent/US20180031487A1/en
Application granted granted Critical
Publication of US10101279B2 publication Critical patent/US10101279B2/en
Expired - Fee Related legal-status Critical Current
Adjusted expiration legal-status Critical

Links

Images

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/87—Investigating jewels
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/251—Colorimeters; Construction thereof
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
    • G01N21/274—Calibration, base line adjustment, drift correction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/061—Sources
    • G01N2201/06113—Coherent sources; lasers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/10—Scanning
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/12—Circuits of general importance; Signal processing

Definitions

  • the present invention relates to a method of diamond color grading, and particularly to a method of diamond color grading by a Raman spectrometer.
  • an object of the present invention is to provide a non-destructive and rapid examination method for the color-grading of diamonds.
  • the method of diamond color grading comprises steps of: providing a Raman spectrometer operating with a laser beam of wavelength 785 nm and total laser energy of 450 mW for an average detection of surfaces of diamonds; six continuous scans being performed on each diamond to obtain an averaged Raman spectrum; a spectral range of the Raman spectrometer used for data acquisition being 100-3300 cm ⁇ 1 ; and each Raman spectrum being processed by background subtraction and peak intensity normalization so as to result in a smooth baseline and calibrated intensity, from which the diamond color is capable of being graded based on a characteristic peak at 2030 cm ⁇ 1 .
  • FIG. 1 a shows a Raman spectrum of diamond in a spectral range of 100 cm ⁇ 1 to 3300 cm ⁇ 1 ;
  • FIG. 1 b shows Raman spectra of diamond in a spectral range of 1800 cm ⁇ 1 ⁇ 2800 cm ⁇ 1 illustrating second-order Raman modes of diamond (2180 cm ⁇ 1 , 2336 cm ⁇ 1 , 2462 cm ⁇ 1 , 2490 cm ⁇ 1 and 2666 cm ⁇ 1 ) accompanying the 2030 cm ⁇ 1 peak. (Zoom in);
  • FIG. 2 a shows Raman spectra of five samples overlaid after the normalized process in the spectral range of 1900 cm ⁇ 1 ⁇ 2700 cm ⁇ 1 ;
  • FIG. 2 b shows Raman spectra of the five samples at the 2030 cm ⁇ 1 peak overlaid, showing that the intensity increases from 931 counts, 1429 counts, 4288 counts, 7816 counts and 10234 counts with the decrease in grade. (E ⁇ F ⁇ H ⁇ K ⁇ L).
  • the signal intensity of a characteristic peak at 2030 cm ⁇ 1 from the Raman spectra of diamond is used.
  • the procedures comprises the technique are detailed below.
  • a total of five GIA certified diamonds (with GIA Reports) with color ranging from E, F, H, K and L are examined as samples in the method of the present invention.
  • the Raman spectrometer ProTT-EZRaman-A6 is used.
  • the wavelength of the laser beam and the power used for the experiment are 785 nm and 450 mw, respectively.
  • a laser spot covers a spatial resolution exceeding 100 ⁇ m on the surface of diamond, which allows a homogeneous sampling of the Raman signal.
  • the spectral range of the spectrometer used for data acquisition is 100 ⁇ 3300 cm ⁇ 1 .
  • six scans on different spots are performed to obtain an averaged Raman spectrum for further analysis.
  • Each Raman spectrum is processed by background subtraction and peak intensity normalization through a specific program. This resulted in a Raman spectrogram with a smooth baseline and calibrated intensity ( FIGS. 1 a and 1 b ).
  • the Raman characteristic peak of an ordinary diamond corresponding to the vibration mode of the C—C bond, is at 1332 cm ⁇ 1 .
  • another peak at 2030 cm ⁇ 1 ( FIGS. 1 a and 1 b ) is used as a clue for the color-grading of diamonds.
  • the intensity of the 2030 cm ⁇ 1 peak increases with the more yellowish tint of natural untreated diamonds.
  • normalization of intensity i.e., by comparing the 2030 cm ⁇ 1 peak with a reference Raman mode, is required.
  • the intensity of the 1332 cm ⁇ 1 peak is too high to be used as reference for the normalization of the intensity of 2030 cm ⁇ 1 peak.
  • FIG. 2 a a characteristic second-order Raman peak of diamond at 2462 cm ⁇ 1 which shows up invariantly accompanying the 2030 cm ⁇ 1 peak in each specimen, is used as reference for normalization.
  • the intensity of the 2030 cm ⁇ 1 peak after being processed by normalization against the second-order Raman modes of diamond (more specifically, against the 2462 cm ⁇ 1 peak), exhibits a positive correlation with the yellowish tint of diamond (from colorless to yellowish white) and a negative correlation with their color-grades ( FIG. 2 a and FIG. 2 b ).
  • the stronger intensity corresponds to a much deeper yellow color which represents a much lower grade of diamond.
  • the Raman peak of diamonds at 2030 cm ⁇ 1 is considered as the N-related bond due to the presence of nitrogen impurity in the natural untreated diamonds. It is reported that some C—N related compounds, such as Pb (SCN) 2 , show C—N bonding vibration mode at ⁇ 2030 cm ⁇ 1 .
  • the use of the Raman spectra in the method of the present invention has the advantages of being non-destructive, no requirement for sample treatment and rapidity in analysis. Furthermore, it is based on scientific criterion. It may serve as a novel and semi-quantitative method in complementary to the conventional colorimetric method.
  • the main features of the method of the present invention are as follows: 1. after the correction and normalization, the Raman characteristic peak of diamonds at 2030 cm ⁇ 1 can be used to grade the diamond, and further provides quantitative data for a scientific, objective, orderly and auxiliary color-grading method; 2. the method of the present invention can be applied for the color grading of both loose and inlaid diamonds and for diamonds of all sizes.

Landscapes

  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Biochemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Abstract

A non-destructive and rapid examination method is proposed for the color-grading of diamonds. A characteristic Raman peak of diamond, after being properly processed, can be used for this purpose. This novel method can be applied to color-grading of diamonds of both loose and mounted ones with satisfactory results.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a method of diamond color grading, and particularly to a method of diamond color grading by a Raman spectrometer.
2. Related Art
According to the grading scheme of the Gemological Institute of America (GIA), “white” diamonds are classified into 23 grades, ranging from colorless (D) to pale yellow (Z). The exact color grade of a diamond significantly affects its quality and price. A traditional method of evaluating color grade is carried out by comparing the color of the sample to a set of reference stones. This traditional grading method is much more dependent on the distinguishing capabilities of individual's eyes. Also, it is inconvenient or unsuitable for the grading of inlaid diamonds. Therefore, it is a pressing issue that the existing technical problems as mentioned above are needed to be solved by providing a creative and innovative method for the purpose of grading the color of both loose and mounted diamonds.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a non-destructive and rapid examination method for the color-grading of diamonds.
To achieve the above-mentioned object, the method of diamond color grading comprises steps of: providing a Raman spectrometer operating with a laser beam of wavelength 785 nm and total laser energy of 450 mW for an average detection of surfaces of diamonds; six continuous scans being performed on each diamond to obtain an averaged Raman spectrum; a spectral range of the Raman spectrometer used for data acquisition being 100-3300 cm−1; and each Raman spectrum being processed by background subtraction and peak intensity normalization so as to result in a smooth baseline and calibrated intensity, from which the diamond color is capable of being graded based on a characteristic peak at 2030 cm−1.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a shows a Raman spectrum of diamond in a spectral range of 100 cm−1 to 3300 cm−1;
FIG. 1b shows Raman spectra of diamond in a spectral range of 1800 cm−1˜2800 cm−1 illustrating second-order Raman modes of diamond (2180 cm−1, 2336 cm−1, 2462 cm−1, 2490 cm−1 and 2666 cm−1) accompanying the 2030 cm−1 peak. (Zoom in);
FIG. 2a shows Raman spectra of five samples overlaid after the normalized process in the spectral range of 1900 cm−1˜2700 cm−1; and
FIG. 2b shows Raman spectra of the five samples at the 2030 cm−1 peak overlaid, showing that the intensity increases from 931 counts, 1429 counts, 4288 counts, 7816 counts and 10234 counts with the decrease in grade. (E→F→H→K→L).
 DESCRIPTION OF THE PREFERRED EMBODIMENTS
To provide quantitative data for the color-grading of diamonds, the signal intensity of a characteristic peak at 2030 cm−1 from the Raman spectra of diamond is used. The procedures comprises the technique are detailed below. A total of five GIA certified diamonds (with GIA Reports) with color ranging from E, F, H, K and L are examined as samples in the method of the present invention.
Throughout the experiment, the Raman spectrometer ProTT-EZRaman-A6 is used. The wavelength of the laser beam and the power used for the experiment are 785 nm and 450 mw, respectively. Using multi-mode laser specification, a laser spot covers a spatial resolution exceeding 100 μm on the surface of diamond, which allows a homogeneous sampling of the Raman signal.
The spectral range of the spectrometer used for data acquisition is 100˜3300 cm−1. In each sample, six scans on different spots are performed to obtain an averaged Raman spectrum for further analysis. Each Raman spectrum is processed by background subtraction and peak intensity normalization through a specific program. This resulted in a Raman spectrogram with a smooth baseline and calibrated intensity (FIGS. 1a and 1b ).
The Raman characteristic peak of an ordinary diamond, corresponding to the vibration mode of the C—C bond, is at 1332 cm−1. However, instead of the C—C mode, another peak at 2030 cm−1 (FIGS. 1a and 1b ) is used as a clue for the color-grading of diamonds. In this study, it is noted that the intensity of the 2030 cm−1 peak increases with the more yellowish tint of natural untreated diamonds. In each specimen, in order to be quantitative, normalization of intensity, i.e., by comparing the 2030 cm−1 peak with a reference Raman mode, is required. The intensity of the 1332 cm−1 peak is too high to be used as reference for the normalization of the intensity of 2030 cm−1 peak. Instead, Some minor peaks in the Raman spectrum in spectral range between 1600 cm−1 and 2800 cm−1, with their intensity comparable to that of 2030 cm−1 peak, are suitable for the normalized purpose (FIG. 2a ). In FIG. 2a , a characteristic second-order Raman peak of diamond at 2462 cm−1 which shows up invariantly accompanying the 2030 cm−1 peak in each specimen, is used as reference for normalization.
In the present research, the intensity of the 2030 cm−1 peak, after being processed by normalization against the second-order Raman modes of diamond (more specifically, against the 2462 cm−1 peak), exhibits a positive correlation with the yellowish tint of diamond (from colorless to yellowish white) and a negative correlation with their color-grades (FIG. 2a and FIG. 2b ). In other words, the stronger intensity corresponds to a much deeper yellow color which represents a much lower grade of diamond.
To date, there is few research or analysis on the Raman peak of diamonds at 2030 cm−1. The Raman peak of diamonds at 2030 cm−1 is considered as the N-related bond due to the presence of nitrogen impurity in the natural untreated diamonds. It is reported that some C—N related compounds, such as Pb (SCN)2, show C—N bonding vibration mode at ˜2030 cm−1.
As described above, it is clear that the use of the Raman spectra in the method of the present invention has the advantages of being non-destructive, no requirement for sample treatment and rapidity in analysis. Furthermore, it is based on scientific criterion. It may serve as a novel and semi-quantitative method in complementary to the conventional colorimetric method.
Accordingly, the main features of the method of the present invention are as follows: 1. after the correction and normalization, the Raman characteristic peak of diamonds at 2030 cm−1 can be used to grade the diamond, and further provides quantitative data for a scientific, objective, orderly and auxiliary color-grading method; 2. the method of the present invention can be applied for the color grading of both loose and inlaid diamonds and for diamonds of all sizes.
It is understood that the invention may be embodied in other forms within the scope of the claims. Thus the present examples and embodiments are to be considered in all respects as illustrative, and not restrictive, of the invention defined by the claims.

Claims (1)

What is claimed is:
1. A method of a diamond color grading, comprising steps of:
providing a Raman spectrometer operating with a laser beam of wavelength 785 nm and total laser energy of 450 mW for an average detection of surfaces of diamonds;
six continuous scans being performed on each diamond to obtain an averaged Raman spectrum;
a spectral range of the Raman spectrometer used for data acquisition being 100-3300 cm−1; and
each Raman spectrum being processed by background subtraction and peak intensity normalization so as to result in a smooth baseline and calibrated intensity, from which the diamond color is capable of being graded based on a characteristic peak at 2030 cm−1 such that a stronger intensity corresponds to a much deeper yellow color which represents a much lower grade of diamond.
US15/083,308 2016-03-29 2016-03-29 Method of diamond color grading Expired - Fee Related US10101279B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US15/083,308 US10101279B2 (en) 2016-03-29 2016-03-29 Method of diamond color grading

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US15/083,308 US10101279B2 (en) 2016-03-29 2016-03-29 Method of diamond color grading

Publications (2)

Publication Number Publication Date
US20180031487A1 US20180031487A1 (en) 2018-02-01
US10101279B2 true US10101279B2 (en) 2018-10-16

Family

ID=61009579

Family Applications (1)

Application Number Title Priority Date Filing Date
US15/083,308 Expired - Fee Related US10101279B2 (en) 2016-03-29 2016-03-29 Method of diamond color grading

Country Status (1)

Country Link
US (1) US10101279B2 (en)

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160109374A1 (en) * 2014-10-18 2016-04-21 Dong-Shyogn Pan Examination method for distinguishing between natural diamond and synthetic cvd/hpht diamonds

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160109374A1 (en) * 2014-10-18 2016-04-21 Dong-Shyogn Pan Examination method for distinguishing between natural diamond and synthetic cvd/hpht diamonds

Also Published As

Publication number Publication date
US20180031487A1 (en) 2018-02-01

Similar Documents

Publication Publication Date Title
Frank et al. Characterization of human breast biopsy specimens with near-IR Raman spectroscopy
Fiore et al. High-extinction virtually imaged phased array-based Brillouin spectroscopy of turbid biological media
US9581553B2 (en) Examination method for distinguishing between natural diamond and synthetic CVD/HPHT diamonds
US20080129992A1 (en) Apparatus For Depth-Selective Raman Spectroscopy
US7268330B2 (en) Apparatus and method for defining illumination parameters of a sample
CA2937696A1 (en) Method of spectroscopic analysis of a diamond and apparatus thereof
Beck et al. Non-destructive portable analytical techniques for carbon in situ screening before sampling for dating prehistoric rock paintings
US9784687B2 (en) Examination method to apprais corundum that has undergone beryllium diffusion treatment
Osticioli et al. Fluorescence and Raman spectra on painting materials: reconstruction of spectra with mathematical methods
EP3376211A1 (en) Method of diamond color grading
Vítek et al. Raman imaging of microbial colonization in rock—some analytical aspects
US10101279B2 (en) Method of diamond color grading
Shea et al. Bone tissue fluorescence reduction for visible laser Raman spectroscopy
Ruiz-Moreno et al. Raman laser fibre optic strategy for non-destructive pigment analysis. Identification of a new yellow pigment (Pb, Sn, Sb) from the Italian XVII century painting
US8159665B2 (en) Apparatus and methods for fluorescence subtraction in Raman spectroscopy
WO2023066158A1 (en) Establishment of non-marking quantification method for detecting lung tissue collagen
Barbillat et al. Demonstration of low‐frequency performance and microanalysis capability of multi‐channel Raman spectroscopy with near‐infrared excitation. I
JP2001159610A (en) Emission spectroscopic analyzing method
Sessa et al. Evaluation of MidIR fibre optic reflectance: Detection limit, reproducibility and binary mixture discrimination
Deljanin et al. Characterization of pink diamonds of different origin: Natural (Argyle, non-Argyle), irradiated and annealed, treated with multi-process, coated and synthetic
Tsai et al. Rapid detection of color-treated pearls and separation of pearl types using fluorescence analysis
US20070008525A1 (en) Method for Raman imaging of semiconductor materials
Lo et al. Simultaneous, Submicron Infrared and Raman Microspectroscopies for Effective Failure and Contamination Analyses
Wahl et al. Raman spectroscopic analysis of fresh tissue samples from brain tumors
CN110779924B (en) System and method for identifying emerald

Legal Events

Date Code Title Description
STCF Information on status: patent grant

Free format text: PATENTED CASE

FEPP Fee payment procedure

Free format text: MAINTENANCE FEE REMINDER MAILED (ORIGINAL EVENT CODE: REM.); ENTITY STATUS OF PATENT OWNER: SMALL ENTITY

LAPS Lapse for failure to pay maintenance fees

Free format text: PATENT EXPIRED FOR FAILURE TO PAY MAINTENANCE FEES (ORIGINAL EVENT CODE: EXP.); ENTITY STATUS OF PATENT OWNER: SMALL ENTITY

STCH Information on status: patent discontinuation

Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362

FP Lapsed due to failure to pay maintenance fee

Effective date: 20221016